Recently my kids and I were denied access to our flight because we missed the check in window. We were informed that new calculations would have had to have been made by the pilot, despite not having had any check in luggage. When are these calculations made? Before or after the passengers board? Apparently, our names did not make the manifest in time, despite nobody having boarded the plane yet. We were left stranded at the gate. Can anybody explain the procedures regarding these calculations, because I cannot understand why we were not permitted to fly?
You're really asking two questions here
1) What is the procedure (ie when are the calculations made)?
2) Do additional passengers affect the weight?
What is the procedure
As soon as check in closes, the numbers for passengers and bags is finalized - nothing else can be added to the plane, otherwise it could potentially run out of fuel. Passengers can be removed, but the captain must be informed in case it affects balance.
At this point the captain calculates the required information for weight, fuel, and balance. It's done shortly after check in closes as there is a limited window in which to add extra fuel etc - remember that the tanker needs to be long clear before the engines can be started and other departure checklists can be run.
This is done so early because the pilot needs time to prepare the aircraft for departure, he doesn't have time to mess about later on adjusting the numbers, and if he has to re-calculate later it adds a whole extra area where mistakes can be made - especially since later on the pilot is likely to be more distracted. Doing it once is fairly easy, you plug the number of passengers into a set of sums along with temperature and other related factors, and it works fuel load out for you. If you try adding passengers you have to re-calculate this, then work out how much extra to add... it's just a whole bunch of extra things that can go wrong.
Do extra passengers affect the weight/balance of the aircraft
Short answer: yes
Take an A319 as an example aircraft: empty, it weighs 40,000 kg, up to a maximum of around 60,000kg
Now I have no idea what you and your family and bags weigh, but let's produce a range. Please don't be insulted by the range: the airline aren't judging your weight when deciding if you can board late: they have to have a single rule regardless of whether it's a skinny teenager travelling alone or a party of 15 obese people
- You're an adult, so you presumably weigh anywhere between 50 and 150kg
- You said children but don't state an age, so they could be newborns or adults: weight anywhere between 2kg and 150kg
- I don't know how many children you have, but for the sake of argument I'll guess it's between 2 and 5 (as you said "children") - that's somewhere between 4 and 750kg
So your total weight for a single family is anywhere between 54kg and 900kg. Chances are most families are more like 250-300kg (a couple of adults at 60-100kg each, and a couple of kids at 20-40kg), but airlines have to assume worst case, otherwise their check in staff have the impossible job of deciding who's too fat to board late.
So take that worst-case scenario (6 obese people) and add a 7kg carry-on bag each, that's nearly 1000kg of weight which the pilot doesn't know on the plane. Or over 2% of the aircraft's empty weight and nearly 1.5% of the maximum takeoff weight. This is assuming they have no hold bags.
Even if your family only weighs 250kg between you and your bags, that's still nearly 0.5% of the aircraft's empty weight - a not insignificant number.
And finally you have to remember that by carrying the extra 0.5% of weight in people, the aircraft needs some extra fuel. And a bit more fuel to carry that extra fuel, and both of those extra amounts of fuel change the balance of the aircraft.
In most "normal" flights you aren't going to make a huge enough difference to balance to cause a crash, or change the fuel requirement enough to cause an issue, but if the aircraft had to divert, you could be the difference between running out of fuel or not, and in some worst-case circumstances a really big family could upset a small aircraft.
The Advisory Circular "AIRCRAFT WEIGHT AND BALANCE CONTROL" (AC120-27E) describes one way in which passenger weights and baggage weights may be calculated by the airlines for various passenger populations, aircraft sizes and configurations, and season (summer or winter, because of the effects of density altitude).
What may have happened is that they had already calculated W&B for the flight, loaded a certain amount of fuel for the passenger and cargo weight, flight plan, and weather, and didn't want to (or couldn't) recalculate.
You didn't say what kind of aircraft you were flying on, but you should know that the smaller or lighter the airplane, the more sensitive it is to weight and balance. When I've flown on a Dash-8, a certain number of passengers had to be fore, abeam, and aft of the wing in order to maintain the center of gravity. On a larger aircraft such as a 747, there is more flexibility with W&B.
I was in aviation many years in 3 countries in Traffic/Dispatch/Load Control (weight&Balance).
As most say on here the smaller aeroplanes are more balance critical.
I used to take great pride in getting an aeroplane closed up and ready for push back on schedule. I also used to take great pride in getting late pax on board and still getting a schedule. The loadsheet has a box at the bottom labelled LMC. Last Minute Changes. There is a specific weight allowed, dependent on aircraft, acceptable without having to recalculate. But a competent loadsheet officer should be able to within a very short period.
Flying is not the pleasure it used to be, security has made it far more complex. I was denied boarding recently in Sofia, check in was just closing as I arrived and the last pax just going through security. The EasyJet aeroplane had not even taxied on to stand and it had a thirty minute turnround. I had no baggage. Imagine how angry I was, knowing the system, knowing that checking me in would make no difference to the departure. To have a check-in agent telling me the Captain had already completed pre-departure procedures and would not allow a late pax. It was absolute bull, despite how cross I was I knew it was pointless getting angry at check in but internally I was seething.
The next flight to MAN wasn't until the following day so it was either a hotel or flight to London and then train to MAN. Of course these cheap airlines do not give refunds or transfer so it was a new ticket at great expense. There-in lies the crux in my opinion. I would suggest that the executives at the head of companies such as EasyJet have the policy as a way to increase revenue. At small airports such as Sofia it takes hardly any time to pass through, security & immigration. Obviously the bigger the airport the more time it takes. Gone are the days when a breathless Pax Agent would arrive at the gate 10 minutes before push back saying, please can you get these late pax on?